N2O Emissions During Establishment Phase of Various Bioenergy Cropping Systems
As bioenergy cropping systems are developed, their greenhouse gas (GHG) emissions will be a key component of sustainability evaluations. Nitrous oxide (N2O) is a potent GHG and a substantial proportion of the total GHG footprint associated with feedstock production. N2O emitted from soils is primarily the result of microbial activities, which are influenced by various environmental factors including temperature and oxygen and water availability. The impact of each of these factors differs among various cropping systems. To understand how traditional and biomass feedstock cropping systems might vary with regard to N2O emissions, researchers at the Department of Energy’s Great Lakes Bioenergy Research Center compared the establishment phase N2O emissions of annual monocultures of continuous corn and corn-soybean-canola rotations; perennial monocultures of switchgrass, Miscanthus, and hybrid poplar; and perennial polycultures of early successional species, native grasses, and native prairie species. Measurements were done over a 2- to 4-year period following planting over which several perennial crops attained “full capacity” biomass production. They found that during the establishment phase, perennial bioenergy crops emit less N2O than annual crops, especially when not fertilized. Emissions for perennials were about three times less than for annuals on a per hectare basis. N2O peak fluxes were associated with periods of rain following fertilizer application. And finally, the results show that simulation models trained on single systems performed well in most monocultures but worse in polycultures, which means models including N2O emissions should be parameterized specifically for particular plant systems. The results suggest that perennial biomass feedstock cropping systems have the potential for a lower GHG burden even during their establishment phase.
Oates, L. G., D. S. Duncan, I. Gelfand, N. Millar, G. P. Robertson, and R. D. Jackson. 2015. “Nitrous Oxide Emissions During Establishment of Eight Alternative Cellulosic Bioenergy Cropping Systems in the North Central United States,” Global Change Biology Bioenergy, DOI: 10.1111/gcbb.12268.